Surveillance cameras are commonly used for monitoring an area under surveillance, which may be in a remote location. The still or video images captured by a surveillance camera may be monitored in real-time, recorded for later inspection, or both. A surveillance camera may be placed outdoor and operate 24 hours a day. During daytime, sunlight is the primary illumination source providing visible light. During nighttime, illumination is often provided by a manmade infrared light source. Accordingly, a surveillance system should be sensitive to visible light during the day and infrared light during the night.
However, sunlight contains both infrared radiation as well as visible light. Thus the captured images may contain both visible light images and infrared images, which may not be identical. During the day time, visible light only images are desirable. The captured infrared images, which interfere with visible light images, often introduce faulty color reproduction to visible light images and may reduce the clarity and quality of visible light images. During the night time, since only infrared light is present, which is provided by an infrared light source, only infrared images are captured. No visible light images are captured that may dramatically reduce the signal-to-noise ratio of the captured images.
One conventional approach to address the above problems of image degradation uses two dedicated cameras—one for capturing visible light images and the other for capturing infrared images. The visible light camera is provided with an optical filter for blocking infrared light while the infrared camera is provided with an optical filter for blocking visible light. The expense and complexity associated with two cameras is a disadvantage.
Another approach uses only one camera having a mechanical switch to select one of two optical filters. During the daytime, an optical filter blocking infrared light is moved into the optical path while an optical filter blocking visible light is removed from the optical path. During nighttime, the optical filter blocking infrared light is removed from the optical path and the optical filter blocking visible light is moved into the optical path. A disadvantage is that an expensive and failure prone mechanical switch is required to move optical filters.